How to model the three aortic valve domes with polygons?
A possibility to model it is to start from the idea that half of a subdivided cube is nearly half a sphere:

From that, we can take a circle as guide, subdivide the cube and adjust vertices to conform to a third of the guide:

Once ok with it, duplicate it twice around the circle centerr:

Join them, add an edge loop at the junction, close the center. Then rip from the center in order valves to be separated:

Add a solidify modifier.

Extrude, clean the junctions to the artery:

Steps included in the file: